Annual Review of Cold Atoms and Molecules

The following sections are included:

• PREFACE

• FOREWORD

• CONTENTS

The following sections are included:

• Introduction

• All-Optical Formation of Quantum Degenerate Gases of Ytterbium
  • A route toward quantum degeneracy of Yb
  • Quantum degenerate gases and mixtures with Yb
  • Mixtures of Alkali-earth-metal-like atoms and Alkali-atoms

• Quantum Many-body Physics of Yb Atoms in an Optical Lattice
  • Superfluid (SF)-Mott insulator (MI) transition
  • Dual Mott insulators of bosons and fermions
  • A Fermi-Fermi mixture in an optical lattice

• Photoassociation of Ultracold Ytterbium Atoms
  • ¹S₀–¹P₁ photoassociation spectroscopy
  • ¹S₀–³P₁ photoassociation spectroscopy
  • Special case: Dicke’s subradiant state
  • Two-color photoassociation spectroscopy
  • Optical Feshbach resonance

• Summary

• Acknowledgments

• References

Ultracold polar molecules trapped on an optical lattice is a many-body system that, under appropriate conditions, may support collective excitations reminiscent of excitons in solid state crystals. Here, we discuss the rotational excitations of molecules on an optical lattice leading to rotational Frenkel excitons. Apart from solid hydrogen, there is no other natural system that exhibits rotational excitons. The rotational excitons have unique properties that can be exploited for tuning exciton–exciton interactions and exciton-impurity scattering by applying an external electric field. We show that this can be used to explore the competing role of the dynamical and kinematic exciton–exciton interactions in excitonic energy transfer and to study quantum localization in a dynamically tunable disordered potential. The rotational excitons can also be used as a basis for quantum simulation of condensed matter models that cannot be realized with ultracold atoms. As an example, we discuss the possibility of engineering the Holstein model with polar molecules on an optical lattice.

In this chapter, we have reviewed our recent theoretical advances in quantum phase transition of cold atoms in optical lattices, such as triangular lattice, honeycomb lattice, and Kagomé lattice. By employing the new developed numerical methods called dynamical cluster approximation and cellular dynamical mean-field theory, the property in different phases of cold atoms in optical lattices is studied, such as density of states, Fermi surface and double occupancy. On triangular lattice, a re-entrant behavior of phase translation line between Fermi liquid state and pseudogap state is found due to the Kondo effect. We find that the system undergoes a second-order Mott transition from a metallic state into a Mott insulator state on honeycomb lattice. Two novel phases are found in triangular Kagomé lattice called plaquette insulator and Kondo metal, which are induced by interaction and asymmetry. The stability of quantum spin Hall phase towards interaction on honeycomb lattice with spin-orbital coupling is systematically discussed. And we investigate the transition from quantum spin Hall insulator to normal insulator in Kagomé lattice which includes a nearest-neighbor intrinsic spin-orbit coupling and a trimerized Hamiltonian. In addition, we propose the experimental protocols to observe these phase transition of cold atoms in optical lattice.

In this chapter, we present, with simplicity in mind, the physics of three-dimensional Bose gases at large positive scattering lengths. We review the different experiments conducted in the dilute limit and beyond, highlighting the recent experimental evaluation of the fermionization ratio of a Bose gas near unitarity and the role of three-body physics. We also present theoretical advances recently carried out to understand upper branch physics near resonance. While this review focuses on the results obtained within a recently developed non-perturbative self-consistent method, we contrast and compare these results with ones derived using other approaches. We particularly emphasize that, within this novel theoretical framework, one predicts, in the zero-temperature limit, that the interaction between condensed atoms for positive scattering length near resonance can be effectively attractive. Finally, we propose a few possible directions to further explore the physics of quantum gases near Feshbach resonances.

Ultracold neutral atoms, with their simple interactions along with well characterized, highly tunable system parameters, are an ideal platform for realizing and then quantitatively studying many-body phenomena. Many-body physics is perhaps most familiar in the setting of condensed matter systems, where the myriad of electrons interacting in the presence of a crystalline lattice give rise to their signature collective effects. Magnetic fields, and gauge fields in general, play an important role in these systems. The integer and fractional quantum Hall effects are iconic examples of physics in electronic systems that rely on magnetic fields. More complex, matrix valued, gauge fields can be used to describe spin-orbit coupling: itself an essential ingredient in many topological insulators, and in spintronic devices. All of these effects rely on the electron’s properties at a fundamental level, and would therefore appear to be absent in neutral atom systems. This chapter describes the techniques we have developed to engineer artificial gauge fields for ultracold neutral atoms using Raman transitions.

The precise and convenient control of quantum states is a major goal in atomic physics and optics, and is expected to lead to new physics and new applications. Several recent methods to manipulate a Bose–Einstein condensate (BEC) are given in this chapter. First, Majorana transition is used to generate a spinor condensate and a multicomponent spinor atom laser. Secondly, a cooperative scattering process as Superradiant Rayleigh scattering, is demonstrated tomanipulate the different momentum state of condensate with some new parameters, such as the variable incident angle, the different frequency components and their initial relative phase, the effective linewidth of laser beams. Thirdly, based on a sequence of standing wave pulses, an efficient coherent control for the specific momentum states and nonadiabatically loading a condensate into the ground state of a one-dimensional optical lattice are demonstrated. Finally, the first-order spatial correlations of a Bose gas released from an optical lattice, and multi-band energy structures of single-particle excitations with zero pseudo-momentum transfer for a wide range of lattice depths are measured.

Bose–Einstein condensates of dilute gases are well-suited for investigations of vortex dynamics and turbulence in quantum fluids, yet there has been little experimental research into the approaches that may be most promising for generating states of two-dimensional turbulence in these systems. Here we give an overview of techniques for generating the large and disordered vortex distributions associated with two-dimensional quantum turbulence. We focus on describing methods explored in our Bose–Einstein condensation laboratory, and discuss the suitability of these methods for studying various aspects of two-dimensional quantum turbulence. We also summarize some of the open questions regarding our own understanding of these mechanisms of two-dimensional quantum turbulence generation in condensates. We find that while these disordered distributions of vortices can be generated by a variety of techniques, further investigation is needed to identify methods for obtaining quasisteady-state quantum turbulence in condensates.

The implementation of electromagnetically induced transparency (EIT) in a cold Rydberg gas provides an attractive route towards strong photon–photon interactions and fully deterministic all-optical quantum information processing. In this brief review we discuss the underlying principles of how large single photon nonlinearities are achieved in this system and describe experimental progress to date.

The dipole force, which is generally conservative and thus unable to cool or heat a particle’s motion, acquires a dissipative nature when invested with some form of memory. We consider here the use of a single mirror, placed at a suitable distance from the particle, as the delay element or memory. This geometry, which may be considered as the prototype for cavity-mediated cooling, itself offers a realistic cooling mechanism, and for a one-dimensional example we find cooling times of milliseconds and limiting temperatures in the milllikelvin range. The cooling force is in principle applicable to atoms, molecules, particles and nanostructures, and can be enhanced through the use of optical resonances, perhaps plasmonic or geometric in origin, in the mirror, and by the inclusion of gain within the optical feedback path.

The system of quantum degenerate atomic gases coupled to an optical cavity offers the opportunity to explore the light-matter strong interaction in a new quantum regime beyond the conventional cavity quantum electrodynamics. We review recent progress made in the cavity quantum optics with Bose–Einstein condensates (BECs). Special emphasis focuses on cavity mediated atomic dynamics and cavity-assisted quantum measurement. First we explicitly explain how to exploit the cavity coupling to the atomic centre-of-mass motion of a BEC to implement cavity optomechanics, simulate Dicke quantum phase transition and study the interplay between nonlinearity and disorder. Then, we consider the cavity coupling to the internal spin degree of a BEC to implement the spin analogue of cavity optomechanics. Finally we introduce how to implement nondestructive measurement via the cavity and discuss the effect of measurement backaction.

Recent experiments have focused on realizing and studying asymmetric potential barriers for ultracold atoms. Practically speaking, asymmetric barriers, or “atomtronic diodes”, open up newmethods for controlling cold atoms, and possibly methods for laser cooling atoms and molecules that are not amenable to present laser-cooling techniques. More fundamentally, asymmetric barriers are interesting as realizations of the textbook statistical-mechanics scenario of Maxwell’s demon. This chapter reviews experimental progress in this area, as well as some related practical and theoretical issues.

We review recent progress in the understanding of thermalization of isolated quantum systems from the point of view of the eigenstate thermalization hypothesis. After discussing the results on the relaxation of integrable systems, we consider the work on how the systems acquire thermal behavior as the integrability gets more and more strongly broken, and on how the ETH and the thermal behavior are related to quantum chaos, and to the many-body localization perspective on the problem.

The following sections are included:

• General Introduction

• Progress of Cold Atoms Preparation
  • Magneto-optical trap
  • Single atom trap
  • Ion trap

• Progress of Atom Interferometry

• Gravity Measurement Using Atom Interferometry
  • Gravity measurement
  • Gravity gradient measurement

• Rotation Measurement Using Atom Interferometry

• GravitationalWave Detection
  • Gravitational wave
  • Situation and progress
  • Gravitational wave detection using atom interferometer

• Cold Atom Clock
  • Microwave clock
  • Space clock
  • Optical clock
  • Chip based clock

• Determination of the Fundamental Constant
  • Determination of gravitational constant
  • Determination of fine structure constant

• Testing Fundamental Physics
  • Equivalence principle test
  • Local Lorentz invariance test
  • Test of local position invariance
  • Other tests

• Summary

• References

The following sections are included:

• INDEX